1. Field of the Invention
The present invention relates to a rotation phase angle measuring device, and an improvement of a control-protecting devices of an electric power system using this rotation phase angle measuring device, e.g., a frequency measuring device, a synchronizing vector measuring device, an synchronous switching controller (SSC), an automatic synchronizer(ASY) and a phase judging device.
2. Background Art
In recent years, the supply of electric power of high reliability and quality is required as a current within the electric power system becomes complicated. For example, necessity of a performance improvement of a basic device required in control and protection of the electric power system such as a frequency measuring device for monitoring a system frequency of a bus line voltage, etc. in an electric power plant, an electric power substation, etc., a synchronizing vector measuring device for calculating an electric amount from the electric power system at high speed, an synchronous switching controller, a automatic synchronizer, a phase judging device, etc. is raised more and more.
The present inventors have already proposed that a coping method using a rotation vector as a spiral vector theory is useful to improve control and protection performance of the electric power system. This is based on a basic technique for expressing an alternating current voltage and current as a vector rotated in the counterclockwise direction on a complex plane. For example, there is a frequency measuring device as described in patent literature 1 (U.S. Pat. No. 6,985,824). In this frequency measuring device, the voltage of the electric power system is measured in timing for equally dividing one period of a reference wave by 4N (N is a positive integer). A voltage rotation vector having a tip for setting this measured voltage to a real part coordinate, and setting the voltage previously measured 90 degrees to an imaginary part coordinate is then calculated. The length of a chord for connecting the tip of this voltage rotation vector and the tip of a voltage rotation vector located by one before is calculated. A voltage effective value is then calculated from the voltage measured between one timing and timing located by one period of the reference wave before. The frequency of the electric power system is calculated from a phase angle of the voltage rotation vector calculated on the basis of an adding value of the above chord length and the above voltage effective value.
Further, a synchronizing vector measuring device is proposed in patent literature 2 (U.S. Pat. No. 7,006,935). In this synchronizing vector measuring device, in each of the above timings, a voltage instantaneous value is presumed from the above frequency calculated in self timing by using a frequency measuring principle using the above voltage rotation vector. An absolute phase angle is calculated by using this presuming value of the voltage instantaneous value. Thus, a synchronous vector can be measured during a short time of one period of the electric power system.
Further, a pole opening-closing phase controller is proposed in patent literature 3 (Japanese patent publication No. 2006-179323). In this pole opening-closing phase controller, an initial vector is calculated from the calculated frequency and absolute phase angle by using the above synchronizing vector measuring principle. An estimating vector is then calculated in consideration of time required in an estimate and an operation in this initial vector. A control delay time is calculated from this estimating vector and a target vector as a target. An opening-closing pole command signal is then transmitted to a circuit breaker in consideration of this control delay time. Thus, turning-on or interruption of the circuit breaker is controlled by a phase based on the frequency and the absolute phase angle accurately calculated.
Furthermore, an automatic synchronizer is proposed in patent literature 4 (Japanese patent application No. 2006-27866). In this automatic synchronizer, passing time until conformity of voltage phases of both systems intended to be simultaneously turned on from a reference time is estimated from the calculated frequency and absolute phase angle by using the above synchronizing phasor measuring principle. Turning-on time of the synchronizing turning-on is then calculated on the basis of this estimating value, and a synchronizing turning-on operation signal is outputted so that a transient electric current based on the turning-on, etc. are restrained to sufficiently small levels.
However, in each of the above systems of the Background Art, a value located 90 degrees before is used in the imaginary part of the rotation vector. Therefore, when a measuring object frequency is shifted from a reference frequency, a problem exists in that a calculating error of the voltage effective value becomes large so that a measuring error of the absolute phase angle becomes large. Further, errors due to voltage drop, a sudden phase change, etc. are generated. For example, problems exist in that phase is changed by load switching of the system, and the change of the frequency is increased and an erroneous operation is performed by exceeding an operation threshold value of a frequency change relay (UFR or OFR), etc.